Current supply device for resistors of electric furnaces



Y. PEYCHES Aug. 26, 1941.

CURRENT SUPPLY DEVICE FOR RESISTORS 0F ELECTRIC FURNACES Filed July 13, 1939 3 Sheets-Sheet 1 .llllllllllllilvl .ailllparinrliinlinvlli ltiilvv illllialdlaltllulnlvalu:4rlnlndinnlrlruvazrilvri'f INVENTOR YVAN PEYC ES Aug. 26, 1941. PEYCHES 2,253,981

CURRENT SUPPLY DEVICE FOR RESISTORS 0F ELECTRIC FURNACES Filed July 13, 1959 3 Sheets-Sheet 2 INVENTOR YVAN PEYCH 5 BY Ma ATTORNEYS Aug. 26, 1941. Y. PEYCHES 2,253,981 CURRENT SUPPLY DEVICE FOR RESISTORS 0F ELECTRIC FURNACES Filed July 13, '1939 s Sheets-Sheet :5

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Fly. 72%? mvsumk Yww PEYCH 5 av armauevs Patented Aug. 26, 1941 CURRENT SUPPLY DEVICE FOR RESISTORS F ELECTRIC FURNACES Yvan Peyches, Paris, France, assignor to Socicte Anonyme des Manufactures des Glaces a: Produits Chimiques de Saint-Gohain, Chauny & Cirey, Paris, France, a corporation of France Application July 13, 1939, Serial No. 284,151 In France July 28, 1938 9 Claims.

The present invention relates to the problem of heating high temperature electric furnaces by means of heating resistances generally called resistors. It is known that the satisfactory operation and the life of these members-for example bars of graphite or of amorphous carbon depend to a great extent on the atmosphere in which they are intended to operate. It is well known, in particular, that some of such resist.- ors-especially those which, on the other hand, possess the greatest aptitude for heating, such as the above mentioned resistors-frequently undergo at the temperatures in question, of the order of 1600" 0., a detrimental chemical reaction with the atmosphere which is in contact with them.

In order to increase the life of the heating resistances, in particular of those which are formed by bars of carbon, graphite, or other oxidizable materials exposed to an oxidizing atmosphere at the same time as to high temperatures, it has already been proposed to provide special means for making the enclosure of the furnace as fluidtight as possible, or even to enclose these elements in refractory sheaths made of a material which is impervious to gases at the temperature of use. In certain cases, said sheaths are in direct contact with the resistor, and in others theyleave around same an annular space in which is confined an atmosphere that is not detrimental to the heating element. It has also been proposed to make plastic coatings (glass coatings) on the resistors, but such coatings only act as a protector above their softening temperature and consequently allow a lack of protection to remain at the ends which are always colder. 4

The presence of said sheaths, or more broadly, the necessity of making the resistors operate inside a'gas-tight chamber, gives rise to serious mounting 'difliculties, for the solution of which various more or less efficient artiflces have already been proposed.

It is in fact necessary for the enclosure, the resistor and the current supply members as a whole, to be arranged. in such a manner as to provide simultaneously: as perfect an electrical connection as possible between the resistor and said members, the free axial and transverse expansion of the resistor, the permanent fluidtightness of the enclosure round the heating portion of same, and finally, the greatest possible Joule eflect or by reduction of energy K ra; thermic t vity-4n the none of the current lurrtv members.

In the known assemblies, all these conditions are not fulfilled.

For example, in the case of a. resistor provided with a sheath and having no direct contact with same, manufacturers have been led to crimp the current supply members on the sheath, with the interposition of a rigid fluid-tight joint, but it is necessary in this case for the resistor to be able to expand axially, independently of the sheath, owing to the fact that it is practically impossible to find a conducting material and an impervious refractory material which have the same coefficients of expansion.

This requirement has led to the construction of slipping contact members. However, it has been found that these contacts have the drawback of offering a rather high resistance to the passage of the current, which resistance furthermore changes in an unforeseeable manner owing to the rise of temperature and the relative movement of the contacts and of the resistor.

It has also been proposed, in order to permit of the free expansion of a resistor which is protected by a sheath, to cut out said resistor in helical shape, so as to makeit resilient.

The object of the invention is to fulfill the various above mentioned conditions, either in the case of resistors which are directly protected by enclosures of the sheath type, such for example as a fluid-tight sillimanite tube, or in the case of resistors which are not provided with sheaths and as regards which the enclosure of the furnace itself acts as a fluid-tight protector.

The invention consists in constructing the current supply members for resistors of electric furnaces, in the shape of a conducting head which is generally made of metal, is fluid-tightly connected to the enclosure of the resistor, and contains a conducting liquid, for example a molten metal, which bathes the end of the resistor and permits oi the free relative expansion of the resistor and of the other associated members, while ensuring the supply of current to the resistor under far better conditions than those obtained by the juxtaposition of rigid surfaces.

In addition to these main features which it fulfills in all cases, the liquid conductor contained in the current supply head may further, under certain conditions, in particular when th enclosure is formed by a refractory sheath, serve to complete the fluid-tightness between said sheath and the current supply head.

In order further to decrease the heating of the heads and, consequently, the losses by Joule effect dissipation in the ends of the-resistor, a

cavity may be provided at said ends and, into which penetrates the conducting liquid which is a better conductor than the resistor. A similar result can be obtained by graphitization of the ends of the resistor, in combination or not with the replacement of a part of the graphite by the conducting liquid.

The choice of the conducting substance forming the contact bath is guided by the following considerations:

The substance chosen must melt at low temperature and nevertheless have a low vapour tension at the temperature to which the head is raised in normal operation.

Said substance must also be capable of producing a good contact with the resistor and also with the metal forming the current supply head. On the other hand, whether in the liquid or in the vapour state, said substance must not appreciably attack these materials.

One embodiment of the invention consists in using molten tin as a conducting bath, since same iulillls these various technical conditions particularly well, while being satisfactory from the economical standpoint. Furthermore, the use of molten tin as a conducting liquid is particularly advantageous, since when it comes into contact with an oxidizing gas which is capable 01' passing through the joints, the tin oxidizes and stops up said Joints.

The accompanying drawings show various current supply devices possessing the features of the invention.

In said drawings:

Figs. 1 to 3 are dlagrammatical views showing various characteristic embodiments.

Figs. 4 to 8 are views showing longitudinal sections of various modifications 01' construction of gurrent supply devices according to the inven- Fig. 9 shows the application of the invention in the case in which the fluid-tight enclosure has to be formed by the furnace itself.

Fig. 10 is a longitudinal section of a current supply device, in the case in which the resistor is extended at each end by an intermediate part which conducts the current.

Fig. 11 shows an embodiment of the invention in the case in which the resistor is placed vertically.

Figs. 12 and 13 show peculiarities of construction which, for their part, are objects of the invention.

Figs. 1, 2 and 8 show the principle oi the invention, in the case in which the resistor l is enclosed within a sheath 2.

In Fig. 1, according to the invention, each current supply head I is fluid-tightly connected, by the Joint 4, to the sheath 2 and contains a quantity of conducting liquid I, for example tin. The sheath 2 consists of a non-porous material, such as sillimanite, sintered alumina, porcelain and the like. The resistor, which is centred in the sheath by means or a constriction 6 of the current supply head, bathes with its ends in the conducting liquid which transmits to it the current that is supplied to the metal head by a terminal I.

It can be seen that the variations of length of the resistor proportionally to the temperature can be eflected freely owing to the interposition of the liquid bath 8 between the resistor and the current supply head.

The device shown in Fig. 2, which is derived from the previous one, is a particularly advantageous embodiment of the invention, wherein the liquid 5 fills the chamber 3 completely, so that the whole of the end of the resistor "is covered by said liquid, the supply of the current to the resistor being eflected under the best conditions. Furthermore, since said liquid has access to the cement joint 4, it contributes to ensure fluid-tightness under the conditions mentioned above. The liquid is introduced through the opening 3 and the level or the liquid is higher than the joint 4 and the adjacent wall of the joint 3, so that a perfect hydraulic seal is attained.

In this embodiment, the constriction 6 which serves for centring the resistor, is part of a special member fixed on the sheath 2 and carries a joint 8 which is intended to prevent the liquid from penetrating into the annular space between the sheath and the resistor.

It is moreover unnecessary for said joint to be absolutely fluid-tight, since the small quantity of liquid that might succeed in passing into said annular space and in vaporizing therein would recondense inside the colder zonesformed by the chambers 3.

In the exemplary embodiment of Fig. 3, in order to decrease the heating 0! the current supplies by Joule eflect dissipation, the resistor I has been hollowed out over a certain length 0-1). in such a manner that the liquid employed, which in this case is a better conductor than the material of the resistor, substitutes itself for said resistor in the cavity thus provided. Furthermore, this substitution enables, for the same electric conductivity of the ends of the resistor, the crosssection of said resistor to be reduced at its ends and, consequently, the losses by thermlc conductivity to be reduced. The end of the resistor is enclosed by the casing 3 having an opening id for the introduction of the liquid.

In the exemplary practical construction shown in Fig. 4, in order to enable the resistor to be dismounted and extracted, the current supply head is made in two parts I -l which are assembled by screwing. The part 3' is provided with a tube 43 for the introduction of liquid tin. Between the part 3" and the sheath 2 is interposed the joint 4. A graphite bush B, which is vagainstashoulder6oifthepart3"bytheendl.

oi the part I. serves for centring the resistor which is made for example 01 amorphous carbon.

The portion 3* oi the current supply head carrles a plug 40 and screws 4| and 42 engaging the plug ll.

Asuiflcient cooling 0! the current supply head is provided by the fins ill.

Fig. 5 shows a modification by means oiwhich the drawbacks are eliminated which may be caused by an untimely solidification oi the liquid at the rear of the resistor, either when the heating is stopped without taking any precaution, or in the case of too sudden a cooling of the current supply head.

For this purpose, the chamber which is adapted to contain the liquid in the conducting head is limited by the ring I and by a second ring ii through which the resistor At the rear of the ring H is provided a compartment II, by means of which the axial expansion of the resistor can take place jreely.

The cooling of the current supply head is obtalnedintbiscasebymeansoiawateriacket l3 enclosing a chamber 50 which is filled with water.

Fig. 6 shows a practical embodiment of the previous device, in which the liquid is contained in a cartridge I4 which is hooped by the body 8" of the conducting head and is closed by the ring II. A plug 60 is screwed into the body I".

In the example of Fig. 'I, in order to avoid, as in the previous case, the transmission of the current from having to be effected by the contact between the rigid elements 3" and M, the collar 8" and the ring I I are kept spaced apart by means of a cylinder l5 provided with openings l8 through which the conducting liquid 5 is in direct contact with the current supply head. A plug "I carrying the ring II is screwed upon the body 8" which is integral with the collar 2.

Fig. 8 shows a preferred embodiment of the invention, in which the current supply head is formed by the assembly 01' a tube 3, a central body 3 and a rear element 3 forming a plug. The central body 3 has a threaded opening 80 for the introduction of liquid tin.

The joint which is intended to prevent the conducting liquid from passing into the sheath 2 is formed by two rings 8 -8 separated by a sleeve I1, the whole arrangement being held in position and pressed against the refractory tube 2 by the cylinder i5 provided with openings. Clamping is effected by means of the plug 3.

A passage it enables the liquid to, penetrate into the annular chamber I! so that said liquid can thus complete the fluid-tight action of the front joint 4.

Fig. 9 relates to the case in which the resistor I is not provided with a sheath and is mounted inside a furnace l9 which forms a fluid-tight chamber owing to the interposition of a joint 2|) between the current supply head 3 and the lateral wall of said furnace. The resistor is centred by a constriction 6 provided with a joint 8, according to an arrangement similar to that of Fig. 2.

As in the case of 'Fig. 3, a channel a-b is provided in the end of the resistor. The casing} enclosing this end of the resistor is closed by a plug 90 and is provided with an opening ii for liquid tin.

In the example of Fig, 10, which shows a practical embodiment of the arrangement of Fig. 9, each or the ends of the heating part I- of the resistor is electrically connected to the liquid 5 by means of graphite bodies I. In the example under consideration, said bodies are provided with a channel o-b. Between the plug 2" and the body 3 is provided a water Jacket 2| for cooling the end of the current supply head. The convection currents, that occur in the liquid which is hotter in the zone 0-!) than in the zone I, contribute to the cooling of the part I which is in oontactwith the heating element I. The plug 3 is provided with a passage 2 for the liquid.

It is obvious that the principleof mounting current supplies which characterizes the invention applies to the case of a vertical resistor. Fig. 11 illustrates an application of this kind to a resistor provided with a sheath.

This resistor 2, for example an earthenware tube, is sealed at its upperpart in a cup 2 which is made of a current conducting material and contains the conducting liquid I. Said cup is embedded in the arch of the furnace.

At its upper end. the resistor I is screwed in a conducting bell i which rests on ribs 22 of the cup The mister i and the tube 2. which are simply held at their upper part, hang freely in the liquid which is contained in a refractory pot 2' Sealed in the sole of the furnace. A diaphragm 28, for example made of fusible glass, protects the liquid from the action of the atmosphere of the furnace.

The current is supplied to the cup 22 by a cable 24, through the upper liquid 5, then through the resistor, then through the lower liquid 5 and leaves same through the dipping member 25 of a cable 25.

Since the lower part of the bell 3 is partially imersed in the liquid of the cup 22, the outer air cannot penetrate into the enclosure containing the resistor.

In all the above described current supply devices, the replacement of the resistor can be readily eiiected. It is particularly quick and easy to effect in the example of Fig. 11.

It must be observed that, when the furnace is cooled, a drop in pressure occurs in the space between the resistor and the protecting sheath. Bald drop in pressure would be liable to favour a penetration of the conducting liquid into said space, through the Joints 8 of the previous figures.

Fig. 12 shows a means which enables the extent of said drop in pressure to be decreased in the space 21 between the resistor I and the sheath 2. Towards the ends of the resistor. which are cooler than the heating portion, is provided a chamber 28 which communicates, through a channel 29, with the space 21. A chamber 12* surrounding the sheath 2 is also filled with liquid. The volume of said chamber 28 is such that, when the furnace cools, the Pressure in the arrangement 2l28 remains sufficiently near the atmospheric pressure exerted on the conducting liquid, for there to be no tendency for any infiltration of same to occur through the joints 8. However, the decrease of conducting cross-section thus produced opposite said chamber 28 would be. liable to cause an excessive heating in this region. A feature of the invention consists in this case in locally transforming the end 0-11 of the resistor into graphite. which resistor is itself made of amorphous carbon, graphite being a better conductor than amorphous carbon.

This graphitization, which improves the conductivity and therefore decreases the heating at the spots where the graphite is produced, is arivantageously eiifected, as shown in Fig. 13, in the zones 20-30 of the resistor which are placed pposite the supports Ii-JI, on which the proeating sheath 2 may rest.

This partial graphitlzation of the resistors may also be advantageously applied to their ends. In a general manner, said graphitization may be applied whatever be the type of carbon resisters and of current supply members used.

I claim:

1. In electric furnaces, in combination, a resister, an enclosure surrounding said resistor. and spaced therefrom, said resistor having a free uncovered end extending beyond said end e. a conducting head surrounding said end and being spaced therefrom, means constitutin a fluid-tight connection between said conducting bead and said enclosure. and a conducting liquid situated in said head and bathing said end of the M8101. i

2. 1h electric (unseen. in I. resister, as endnsme aid canister and spaced therefrom. said resides. o time, Wed end extending beamd said s Mdvfl'fihfl between said conducting headondsddenclosuzesndmoitenmehlsimttiedhsaidhesdsndibslihinzsaidendofthe resistor.

3. In electric fwmaces, in combination, a re sisnor, m endosure surrounding said. resistor and spaced therefrom, said resistor having s free, uncovered end extending beyond said enclosure. a conducting head surrounding said end and being spaced thEI'ErUlD- means constituting a. fluid tight connection between said conducting head and said enclosure; I- conducting liquid situated in said head bathing saici v end of the resistor, and separate means closing that end of the 811-- ciosure which is siis'uaiied close to said free end of the resistor; the last-mentioned means engagin: said resistor fio' prevent a. penetration of said liquid between said enclosure and said resistor.

4. In electric furnaces, in combination, a resister, an enclosure surrounding said resistor and spaced therefrom, said resistor having a free, uncovered end extending beyond said enclosure, a. conducting head surrounding said end and be ing spaced therelrom, a. conducting liquid situaefledi in said head andbathing. said. end of the resister, and means open to said liquid and constimiiing at fluid-tight connection between said conducting head and said enclosu e.

5 In electric furnaces, in combination. a resister, on surrounding said resistor and spaced therefrom. said resistor having a tree, end extending beyond said enciosure, a conducting surrounding said end and bein: spaced therefrom, means. constituting a fluidtight connection befiween said conducting heed sndsaidenelhsuazmsndamassofmolfientin situated in said head and bathing said end of the resistor.

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holes and adapted to push the rings and the sleeve against the end of? the enclosure, mid eylindrieli body bearing, on the opposiiie side, against the md 08 said pins.

8. In electric in combination with a resistor and. an enclosure containing acid reshtor; a. current dewice. which comprises a conducting head, means for fluid-flghdiy conmeeting said. head to the an intermediate body extending said resisfior and penetrating, into said current sum: heed, a channel provided in said inter body and extending the me. between said body and the i and a mem liq- Bid insaid headl and penetrating mid said chmnei up to we end of some.

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